We prepare to leave at 8am, and outside dawn has just risen over Inner Mongolia. We have been sleeping in a little truckers' roadhouse hotel which we stumbled upon last night, after three hours of marching through the Gobi darkness.

It's Friday, December 9, and seriously cold outside - about minus 20 - although this is made much worse as the Siberian winds are whipping down from the north, biting through our clothes, stinging our faces, and, when we remove our gloves for simple tasks such as tying a shoelace, making our hands go numb in less than 20 seconds.

So we were relieved to find this place to sleep in the warm, and be spared another night in our icy tents. As we stumbled through the door last night, our huge rucksacks sticking in the doorframe, a gaggle of truck drivers looked up from their dinner, understandably surprised to see the arrival of two absurd foreigners in puffa jackets and giant fur Chinese army hats. I tried to break the ice by explaining in my faltering Putonghua that we were English people, to which a quick-tongued driver smiled and replied 'and we are Chinese people', to much laughter. We ate a bowl of noodles and collapsed into bed.

Today, we repack our bags, brace ourselves and walk back out into another mid-winter's morning. We are heading south along the road again, which is good for fast progress, but also not much fun, especially because the trucks which periodically go past often sweep an icy cloud of snow and fumes into our faces.

I call this kind of day a 'miles not smiles' day. For other days this week, we have managed to find much smaller paths and tracks through the hills or alongside the railway. These days are slower but more fun and more interesting - 'smiles not miles'.

Despite our progress being so slow, with us covering only about 30 kilometres of hard-fought ground daily, the landscape has been gradually changing. The flat desert plains of Outer Mongolia and the Chinese border lands have given way to a world of rounded hills, with increasing tufts of shrubs poking through the snow, and even groves of what look to be recently planted trees.

Sign of human habitation are becoming more regular, too. Little farmhouses with sheep pens are visible every few kilometers, and there are plenty of ramshackle, half-abandoned villages, consisting of small brick houses, insulated with mud on the outside.

We wander through them in the middle of the day, dogs barking at us and old men staring at us. I wonder to myself what these elderly folk must have seen in their lifetime, in this remarkable and unpredictable country - a world war, a revolution, the extraordinary to-ing and fro-ing of government policy. And I imagine we are among the first Westerners they have seen walking through here: what do they think of us?

Our progress is also giving us more glimpses of the new China - from the crest of small hills we spot huge chimneys spewing fumes into the cold clear sky. Beside the road, there are petrol stations, newly built towns, and walled compounds of neat, production-line factories.

As we plod on southwards, the weight on our backs feels heavier and heavier. I have a slightly strained shoulder, and the top of my spine and soles of my feet are aching before day's end. My cameraman and expedition partner, Leon McCarron, has a sore left foot and a slightly pulled chest muscle.

The cold wind allows us to take only very short breaks, and so we have only just enough time to eat a handful of crumbled biscuits and drink some lukewarm water from our broken thermos flask. And then we haul on the packs and start walking to warm up again.

Today we have a morale booster - we see a kilometre marker indicating that we have now walked 500 kilometres, which is 10 per cent of our walk home to Hong Kong.

And as evening approaches and the temperatures start to dive, we are relieved to see another little settlement come into view, where the local restaurant owner gives us a cheery welcome, and again has some rooms in which we can sleep. So it has been a good day of miles, and it even ends with a smile.

When the expedition gets tough, and the pain and exhaustion tests me to my limits, thinking of Viva, the children's charity for which this expedition is raising funds, keeps me going.

Rob Lilwall's previous expedition, Cycling Home From Siberia, became the subject of an acclaimed motivational talk, a book, and a National Geographic television series. Every week in Health Post, he will write about the progress of his latest adventure, Walking Home From Mongolia, which is in support of the children's charity Viva. www.walkinghomefrommongolia.com